Heat activated dry silver

ABSTRACT

LIGHT-STABLE SHEET MATERIALS WHICH DARKEN ONLY UNDER RELATIVELY SEVERE HEATING AND ARE RENDERED LIGHT-SENSITIVE AND RAPIDLY HEAT-DEVELOPABLE BY MODERATE HEATING CONTAIN AN IMAGING COMPOSITION CONTAINING AN ORGANIC SILVER SOAP AND A HINDERED PHENOL REDUCING AGENT TOGETHER WITH A SMALL AMOUNT OF A REDUCIBLE HALOGEN COMPOUND HAVING THE ESSENTIAL STRUCTURE -CONX-OR-SO2NX- WHEREIN X IS CHLORINE OR BROMINE.

United States Patent 3,764,329 HEAT-ACTIVATED DRY SILVER James T. Lee, White Bear Lake, Minn., assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn. No Drawing. Filed Jan. 17, 1972, Ser. No. 218,579 lint. Cl. G03c 1/60, N72 US. CI. 96-67 7 Claims ABSTRACT OF THE DISCLOSURE Light-stable sheet materials which darken only under relatively severe heating and are rendered light-sensitive and rapidly heat-developable by moderate heating contain an imaging composition containing an organic silver soap and a hindered phenol reducing agent together with a small amount of a reducible halogen compound having the essential structure -CONX or -SO NX wherein X is chlorine or bromine.

This invention relates to the visible recording of lightirnages, and in particular to normally light-insensitive coatings and coated sheet materials which are rendered lightsensitive and heatdevelopable by brief preliminary heating. The invention makes possible the preparation, storage, and handling under normal lighting conditions of compositions, coatings and sheet materials which in the last-named form may be made light-sensitive by mere heating.

The sheet materials of the invention have particular utility in the preparation of add-on copies, such for example as microfilm, microfiche cards, or other recordmaintaining media. Portions of the total film or card area may be provided with desired indicia by selective activation, image exposure, and development, and without affecting adjacent areas which then may subsequently be similarly imaged for up-dating or adding further data to the record. The sheet thus serves as an easily up-dated permanent record from which copies for immediate or temporary inspection may be made at any time.

U.S. Pat. No. 3,457,075 describes a dry silver sheet material which is light-sensitive and heat-developable. It contains photosensitive silver halide, an organic silver salt, and a reducing agent. Exposure to a light-image generates from the silver halide component a catalyst which accelerates the image-forming reaction between the other two components to make possible the subsequent heat development of the visible image. The photosensitive silver halide is formed by reaction of a source of halide ions with a small proportion of the organic silver salt. The reaction must therefore be carried out, and the products thereafter maintained, in the absence of light.

It has now been found possible to prepare sheet mate rials which initially are substantially insensitive to light but which upon being subjected to moderate heating are found to possess the full light-sensitivity and heat-developability properties of the dry silver products, by incorporating with the light-stable organic silver salt and reducing agent image-forming composition, and in absence of any silver halide, a reducible halogen-containing compound having the essential structure --CONX or SO NX- wherein X may be chlorine or bromine.

3,764,329 Patented Oct. 9, 1973 ice These halogen-containing compounds are not reactive with the silver salt and accordingly may be introduced with the image-forming components prior to spreading and without protection from exposure to light. The composition is applied in liqiud form in a volatile liquid vehicle which is then permitted to evaporate at less than activation temperature, and the resulting dry layer or coated sheet or film is stable to light. Moderate heating above an activation temperature of about C. then causes reduction of the halogen-containing compound, with formation of a halogen source material which reacts with the silver salt to form photosensitive silver halide. Reduction of the halogen-containing compound is achieved at least in part by reaction with the reducing agent of the imageforming composition and may be exclusively by such means although the presence of small amounts of other reducing agents for the halogen-containing compound is not precluded.

Silver salts of long chain fatty acids, such for example as silver stearate or silver behenate, have been found particularly useful in the sheet materials of the invention. Silver behenate, prepared by precipitation with silver nitrate solution from solutions of the sodium soap of commercial behenic acid and if desired, with co-precipitation of minor proportions of the fatty acid, is presently pre ferred. Other organic silver salts useful in the practice of this invention have been mentioned in the aboveidentified Pat. No. 3,457,075.

To be most useful in the sheet materials of this invention, the reducingagents for silver ion must not be so reactive with the organic silver salt as to cause any significant optical change during the heat activation step. Water-insoluble ortho-alkylor -aryl-substituted hindered phenols are found to meet the requirements and to yield sheet materials capable of producing dense black images with substantially no background darkening. Typical examples include 2,6-ditertiarybutyl-4-methylphenol,

2, 2'-methylenebis- (4-methyl-6-tertiarybutylphenol) 2,4,4-trimethylpentyl-bis- (2-hydroxy-3 ,5 -dimethylphenyl) -methane,

bis- 3 5 -di-t-butyl-4-hydroxyb enzyl) -ether,

2,2-methylenebis- (4-ethyl-6-tert-butylphenol 2,2'-methylene-bis (4-methyl- 6- l-methylcyclohexyl) phenol),

2, 6-bis (2-hydroxy-3 '-tert-butyl-5 '-methylb enzyl -4- methylphenol.

The amounts of organic silver salt and of hindered phenolic reducing agent must be sufficient to enable the formation of the desired dense black image and in the interests of economy of materials the amount of silver salt will ordinarily be little if any greater than such amount. Thus the concentration of organic silver salt may be as low as about 50 to 200 mgm. of silver per sq. m. of the coating. Somewhat larger molar amounts of the hindered phenolic reducing agent may be present, particularly where the same reducing agent is required to react with the halogen-containing compound. The amount of the last-named compound will be sufiicient to bring about the conversion of from at least about one to not more than about ten or twelve percent of the silver salt to silver halide, depending on the particular sensitometric characteristics desired; conversion of about three to about eight percent is usually preferred.

Compounds which have been found particularly useful as sources of halide ion for use in the practice of this invention include N bromophthalimide, N bromosuccinimide, N-bromoacetamide, N-bromoacetanilide, N-bromo- 1 (2H) hthalazinone, N,N dibromobenzenesulfonamide, N-bromo-N-methylbenzene-sulfonamide, 1,3 dibromo-4,4-dimethylhydantoin, potassium salt of dibromoisocyanuric acid, trichloroisocyanuric acid. The N-chloro counterparts of many of these compounds have likewise been shown to be useful but less desirable both in their reaction characteristics and in the photographic sensitivity of the resulting sheet. Presently available N-iodo counterparts are too reactive to provide a light-stable sheet. Compounds are preferred which are free of aliphatic unsaturation and of amino or mercapto groups or of other groups the presence of which might be expected to result in uncontrollable light-sensitivity, or spontaneous decomposition, or excessive color, or other deleterious influence.

In addition to the essential components hereinbefore identified, the coatings of the invention will usually contain a film-forming binder, a toner for the silver image, and a photosensitizing dye, and may contain additional components such as wetting agents, antifoam agents, pigments, fillers, etc. Coatings of such compositions may be made on a temporary support and removed therefrom in dry thin film form, but will ordinarily be applied to paper or film substrates which form a part of the final sheet product. The substrate may be primed or subbed for improved bonding or to prevent excessive penetration or for other purposes, and the coating may be further protected with additional surface layers desired. Transparent coatings on transparent film backings or supports are particularly desirable in permitting subsequent copying of data from the imaged sheet by methods involving light projection or contact printing onto a photosensitive receptor.

The sheet material prepared as above described is stable to light and may be left for many days exposed to ordinary room light conditions. When thus exposed and then briefly heated at image development temperature, no visible change occurs in the coating. On subsequent exposure to a light-image followed by further heating, the sheet will be found to undergo extensive darkening at the light-struck areas. Accordingly, it is possible to first activate the sheet by controlled heating in absence of light, and thereafter to expose to a light-image and then develop the image by further controlled heating. The following specific examples will further illustrate these and other features of the invention, which however is not to be construed as limited thereto. Proportions are by weight unless otherwise indicated.

EXAMPLE 1 Silver behenate homogenate (15%) 67 Volatile vehicle (Z-butanone) 60 Binder (polyvinyl butyral) Phthalazinone 1.0 Mercuric acetate 0.35 Developer 3.2 N-bromoacetamide 0.35

'4 mm.) orifice onto 3 mil (.075 mm.) Mylar transparent polyester film and dried in a current of air at room temperature and under normal room light.

A portion of the sheet is heated for ten seconds at 134 C. without visible change. When then exposed to a lightimage from a photo flash lamp and again heated, a visible record is obtained, the light-exposed areas becoming black in appearance. Another portion is first heated for 8-10 seconds at 90-l00 0., exposed to the light image, and heat developed for 10 seconds at 134 C. to provide an equally distinct visible record.

Under continuous exposure to normal artificial room light the unheated sheet remains unchanged for at least several days. When then heat-activated, exposed to lightimage, and heat-developed, the sheet is found to give visible images on a darkened background.

EXAMPLE 2 Silver behenate suspension, gm 100 Methylethyl ketone, ml. 77 Polyvinyl butyral, gm 2 N-bromo-phthalazinone, gm. 0.2 Tetrabromobutane, gm. 1.6 Polyvinyl butyral, gm. 18 Solution of sensitizing dye, ml. 20 Solution of mercuric acetate, ml. 4.0

The silver behenate suspension contains 12 parts of the salt in 88 parts of a 2:1 mixture of methylethyl ketone and toluene. It is homogenized and is gelatinous and nonsettling.

The dye solution contains 0.13 gram of dye per liter of methylethyl ketone. The dye is the blue sensitizer dye identified as 1-carboxymethyl-3-(N-methylbenzothiazolylindy1)-4-thia-2-thiohydantoin. The mercuric acetate solution contains 5% of the salt, dissolved in methanol.

The silver salt suspension, solvent and two grams of binder are mixed together until the binder is dissolved. The remaining components are added in the order indicated with continuous and intermediate mixing. The mixture is coated on polyester film from a 4 mil (0.1 mm.) orifice and dried at C.

A second coating is next applied, at an orifice of 2.5 mils (0.064 mm.), and promptly dried at room tempera- The coated sheets are stable toward light for at least several months under normal room conditions. When first activated by brief heating they are light-sensitive and when then exposed to a light-image and again heated are found to yield high contrast sharp negative reproductions, the light-struck areas becoming a dense black.

Activation may be accomplished by heating above about 90 C., for example for 30 seconds at C., 15 seconds at C., for 5 seconds at C. Develop ment may then be accomplished by heating for 20 seconds at 115 C., 10 seconds at 127 C., or 5 seconds at 143 C. In general, activation involves heating sufficiently to cause reduction of the organic haloamide and formation of a source of halogen reactive with silver but short of incipient darkening or backgrounding; whereas development involves heating sufliciently to obtain maximum contrast at minimum or permissible backgrounding.

Omitting the mercuric salt from the above-described first coat produces a sheet which may be activated and developed at somewhat lower temperatures and which produces images of somewhat lesser optical density.

Substitution of an equal weight of N,N-dibromobenzene-sulfonamide for the N-bromophthalazinone of the 2,2'-methylenebis-(4-methyl-6-tert.butylphenol) 1,1'-thiobis-(2-naphthol) 2-(4-hydroxy-3,S-di-t-butylphenoxy) 6 (n octlythio)- 1,3,5-triazine.

The N-bromophthalazinone is made by a process involving dropwise addition of bromine (14.6 gm.) to a cold solution of 1-(2H)-phthalazinone (13.3 gm.) in aqueous methyl alcohol (500 ml., 50% by volume) followed by dropwise addition of sodium hydroxide solution (3.64 gm. in 50 ml. water). The yellowish-white precipitate, after filtering, washing with methyl alcohol and with n-heptane, and drying in vacuo, melts at about 160 C. with decomposition, and on analysis shows the compositiOn C3H5N2OBI'.

N-chlorophthalazinone is also eifective. This compound is made by gradually mixing 1-(2H)-phthalazinone gm.) into cold aqueous sodium hyprochlorite solution (100 ml., 5% NaOCl), extracting with dichloromethane, drying, and concentrating under reduced pressure to yield a mass of colorless needles which is washed with n-hexane and dried. The product melts at about 142 C. without decomposition and analyzes as C H N OCl.

The mixture is prepared and coated as described in Example 2. Separate portions are then top-coated with solutions of cellulose acetate, phthalazinone and developer, also as described in Example 2, using as specific developers the following compounds:

(A) 2,2-methylenebis(4-ethyl-6-tert-butylphenol) (B) 2,2'-methylenebis-(4-methyl-6-(l-methylcyclohexyl) phenol) (C) 2,4,4 trimethylphentyl-bis(2-hydroxy-3,5-dimethylphenyl)methane.

Activation, exposure and development produce useful images. Sheets A and B tend to give positive rather than negative images when activated or developed at relatively high temperature or for extended periods of time.

EXAMPLE 4 This example illustrates the use of smaller amounts of silver salt in sheet materials similar to those of Example 2. The first coat composition contains 12% silver salt suspension, gm 75 35 Acetone, m1 77 77 Polyvinyl butyral, gm- 2O 20 N-bromophthalazinone, 0. 2 0. 2 Tetrabromobutane, gm... 1. 6 1. 6 Dye solution, ml 20 20 Mercuric acetate solution, ml 2. 5 2. 5

The top coat is as described under Example 3(0). The resulting sheets are stable under prolonged exposure.

Sheet A is activated 5 seconds at 127 C., exposed, and developed 10 seconds at 127 C. to produce a negative print with good contrast and high image density. Sheet B is activated 5 seconds at 143 C., exposed, and developed 15 seconds at 127 C. and produces a less dense image with some darkening in the unexposed background areas.

EXAMPLE 5 Transparent polyester film is sub-coated with a 4 mil (0.1 mm.) thickness of a solution containing N-chlorophthalazinone 1 Polyvinyl butyral 10 Dichloromethane 190 and the sheet is dried at C. It is then coated with a applied at 4 mils (0.1 mm.) and again dried at 80 C. A final topcoat of a solution as described under Example 3(C), completes the construction. The sheet is stable under prolonged room condition exposure. It is activated in 5 seconds at 132 C. and after flash-lamp exposure to a light-image forms a high density black image at the exposed image areas when developed for 10 seconds at 127 C.

EXAMPLE 6 Coated sheet materials are prepared in accordance with the formulas and procedures given in Example 2 except that in the second coat formulations another material is substituted for half of the phthalazinone content. The operating and image characteristics are substantially the same as those obtained with the earlier formulation. The substituents are:

(A) Urea (B) Tetrahydrophthalimide The mixtures exhibit equally as elfective a catalytic effect as the same amount of phthalazinone alone; wherease the lesser amount of any one of these catalytic materials is found to be ineffective.

What is claimed is as follows:

1. Light-stable sheet material which can be rendered photosensitive by heating, characterized by including a stratum containing an organic silver salt and an organic haloamide compound which is non-reactive with the silver salt and which has the essential structure -CONX-- or 4O NX- wherein X is chlorine or bromine, the amount of said haloamide compound being suificient to supply from about one to about 12 moles of said X component for each moles of said silver salt.

2. Light-stable sheet material of claim 1 wherein is included a water-insoluble ortho-substituted hindered phenol reducing agent for silver ion.

3. Light-stable sheet material of claim 2 wherein the amount of said haloamide compound is sufficient to supply from about three to about eight moles of said X component for each 100 moles of said silver salt.

4. Light-stable sheet material of claim 1 wherein said stratum includes a binder for said silver salt and haloamide compound and is supported on a flexible carrier sheet.

5. Light-stable sheet material of claim 4 wherein said stratum and said carrier sheet are transparent.

6. Light-stable sheet material of claim 2 wherein said silver salt and said haloamide are contained in one layer and said reducing agent in an adjacent layer of said stratum.

, 7 8 7. Light-stable sheet material of claim 1 wherein said 3,661,586 5/1972 Jacd'bs 117 36.9 haloamide compound is an N-halophthalazinone. 3,457,075 7/1969 Morgan 96 -67 References Cited NORMAN G. TORCHIN, Primary Examiner 5 v UNITED STATES PATENTS 5 A. T. SURO PICO, Assistant Examine;

3,031,329 4/1962 Win ert 25065 T 3,146,348 8/1964 Woriman 250-65 T US 3,547,648 12/ 1970 Sagawa 96- 114,1 961 14-1, 114-6, 48 HD; 250 -65 T 

